无法弄清楚为什么我在计算中得到空值

Question

So essentially this is a simple loop that should add up for 10 seconds the distance fallen for an object. When I was debugging it I saw it passed and the variables with correct values but when I entered a println statement right after the calculation in my fallingDistance method, the variable "distance" had a value of zero which I do not see how is possible. What am I missing here?

import java.lang.Math;
import javax.swing.JOptionPane;

public class FallingDistance {

    public static void main(String[] args) {
    double distance =0;
        int count = 0;
        double distanceCalc = 0;
        int varTime = 0;
        while (varTime < 10) {
            varTime += 1;
            System.out.println(varTime);
            fallingDistance(varTime);
            distanceCalc += distance;
            JOptionPane.showMessageDialog(null, "The distance travelled is " + distanceCalc + " meters.");
        }

    }

    public static double fallingDistance(int varTime) {

        double gravity = 9.8;
        double distance = Math.pow(((1 / 2) * gravity * varTime), 2);
        System.out.println(gravity);
        return distance;
    }
}

Answer 1

You must assign value to the distance before using it in main!

public class FallingDistance {

public static void main(String[] args) {
double distance =0;
    int count = 0;
    double distanceCalc = 0;
    int varTime = 0;
    while (varTime < 10) {
        varTime += 1;
        System.out.println(varTime);
        distance = fallingDistance(varTime);
        distanceCalc += distance;
        JOptionPane.showMessageDialog(null, "The distance travelled is " + distanceCalc + " meters.");
    }

}

public static double fallingDistance(int varTime) {

    double gravity = 9.8;
    double distance = Math.pow(((double)(1 / 2) * gravity * varTime), 2);
    System.out.println(gravity);
    return distance;
}

Answer 2

Please assign the value returned from fallingDistance(varTime) method to distance .

Your while loop should be rewritten as:

while (varTime < 10) {
    varTime += 1;
    System.out.println(varTime);
    distance = fallingDistance(varTime);
    distanceCalc += distance;
    JOptionPane.showMessageDialog(null, "The distance travelled is " + distanceCalc + " meters.");
}

Also, your 1/2 will always be evaluated to 0 (because its evaluated as integer). The fallingDistance() method should be rewritten as:

public static double fallingDistance(int varTime) {

    double gravity = 9.8;
    double distance = Math.pow((0.5 * gravity * varTime), 2);
    System.out.println(gravity);
    return distance;
}